Seal and method of making



R. c. SHERMUND 2,093,491

SEAL AND METHOD OF MAKING I Filed Oct. 21, 1935 2, V q, M 7 M, i

I Patented Sept. 21, 1937 UNITED STATES PATENT OFFICE SEAL AND METHOD OFMAKING Application october 21, 1935, Serial No. 45,861

3 Claims.

My invention relates to a seal, and more particularly to ametal-to-glass seal and method of forming it so that breakage due tostrain around the seal is greatly reduced. My invention is particularlyapplicable in the sealing of tungsten rods of relatively large diameterthrough glass envelopes to produce a seal which will maintain a vacuumtherein.

Among the objects of my invention are: To

provide a. metal-to-glass seal wherein strains are balanced; to providea metal-to-glass seal having a low breakage factor; to provide a methodof sealing tungsten rods of relatively large diameter through a glassenvelope; and to provide a simple and efficient tungsten-to-glass seal.

My invention possesses numerous other objects and features of advantage,some of which, together with the foregoing, will be set forth in thefollowing description of specific apparatus 2 embodying and utilizing mynovel method. It is therefore to be understood that my method isapplicable to other apparatus, and that I do not limit myself, in anyway, to the apparatus of the present application, as I may adopt variousother apparatus embodiments, utilizing the method, within the scope ofthe appended claims.

Referring to the drawing:

Figure 1 is a longitudinal view partly in section and partly inelevation, showing a preferred form of head.

Figure 2 is a longitudinal view partly in section and partly inelevation, with diagrammatic representation of heating flames, of anintermediate step in forming the seal of my invention.

Figure 3 is a longitudinal view partly :in section and partly inelevation of the finished seal of my invention.

In modern high power transmitting tubes utilized as oscillationgenerators for radio purposes or in allied arts, the necessity arises ofconducting large amounts of current, particularly for Y the purpose ofheating a thermionic cathode, into the interior of an evacuated envelopeand large cross sections are needed in the conductors. Up to a certaindiameter, tungsten wire, for example, seals readily to glass of certaincharacteristics such as that known in the trade as G702? or alliedglasses, and the resultant seal is air-tight. The glasses available,however, are not exactly of the same expansion characteristics astungsten and as a consequence, the larger the lead thatis to be sealedthrough the envelope becomes, the greater the danger of crackage oftheseal in use. Consequently, when leads are to be sealed through theenvelopes of high power transmitting tubes and where the diameter of theleads is greater, for example, than of an inch, special precautions mustbe taken in order that seal breakage be eliminated.

I have chosen as an example for illustrating my seal, a one-eighth inchtungsten rod l and as a first step in the method of making my preferredtype of seal, I fuse upon the tungsten rod a specially formed bead 2.This head is fused onto the rod in the usual manner, and is of specialshape, having ball-shaped ends 3 with an extensive depressed portion 4therebetween. I also prefer that the ends of the bead contacting thetungsten rod I be somewhat in-curved at the point 5 of contact.

I prefer to make the bead somewhat elongated and in case of aneighth-inch rod, I prefer to make the bead approximately one inch longand the diameter of the ball-shaped ends approximately three times thediameter of the rod.

The next step in forming my seal is illustrated in Figure 2, where aglass tube 6 is positioned with one end 1 directly over the depressedportion {of the bead, and heating flames 8-4 are applied so as to heatboth the central portion of the bead and the end of the glass tube. Thepressure of the flames will cause the end of the tube I to turn in andcontact the central'portion 4 of the bead, and after fusion has takenplace at this point, air pressure is applied to the opposite end of theglass tube 6 so that an enlarged head 9 is formed adjacent the bead.This air pressure is preferably applied before any great length of thetube 6 fuses to the beads so that the junction Ill between the bead andthe tube has approximately the same curve on each opposite surface ofthe tube 6 where it joins the head at end 1 of the tube 6, and thus,leaves the bead at approximately right angles thereto.

Extra glass at point of fusion is drawn into the head 9, thus preventingheavy sections at the bead center. There is thus formed a symmetricalseal and all the glass surfaces leave the tungsten rod at approximatelyright angles thereto and the 'glass of the tube 6 leaves the bead atapproximately right angles thereto. There is a balanced amount of glasson both sides of the junction l0 and thus there can be no unequalheating of the glass at this point in tube operation.

The seal has proved itself in practice to withstand large amounts ofheat without any danger of cracking whatsoever and I have been able toseal tungsten rods as large as one-quarter inch in diameterthrough aglass envelope in this manner without air leakage through the seal andwithout cracking of the seal in operation.

It is obvious that the open end of the tube 6 may be sealed to the mainenvelope of the device in which the seal is to be used in any convenientmanner, as is well known in the art.

I claim:

1. A seal comprising a tungsten rod, a glass wall sealed to said rod,and glass extensions extending in opposite directions and an equaldistance from said seal along said rod, and sealed thereto, saidextensions having enlarged terminals.

2. A seal comprising a tungsten rod, a glass

